We have recently reported the identification and characterization of a gene defect causing Waardenburg Syndrome in a large Brazilian family (Baldwin, et al., 1991). This disease is characterized by hearing loss, pigmentary disturbances, dystopia canthorum and an increased frequency of neural tube defects such as spina bifida. This is the first demonstration of a mutation causing Waardenbury Syndrome as well as one of the first mutations causing a form of congenital deafness. The mutation was found in the human Pax3 gene, a member of the paired domain and homeo domain family of proteins known to bind DNA and regulate gene expression. The goal of this project is to characterize the range of mutations in human Pax3 that cause Waardenburg syndrome and to determine the effect mutations have on protein function. The specific aims of the project include completing the cDNA and gene structure of the human Pax3 gene and to develop PCR based assays to detect mutations in the human Pax3 gene. Secondly, to determine the effect mutations have on DNA binding properties of human Pax3 and to identify other genes that may be targets of human Pax3 action. In conclusion, identification of the Waardenburg Syndrome gene and future characterization of its gene product is likely to increase our understanding of the pathogenesis of this disorder and may enable, for the first time, an opportunity to prevent deafness.